Why couldn't he sell them on an exchange? Take a look at this volume chart...
https://bitcoinaverage.com/charts#USD-volumes-1m
Most days see more than 10,000 bitcoins traded for USD, sometimes more than 30,000 bitcoins. The 30th of August saw more than 70,000 bitcoins traded for USD in a single day.
Although, that's the combined volume for a whole bunch of different exchanges, but there shouldn't be a problem if he gradually sells them off in a couple of different exchanges over several months.
Hell, if he's willing to sell them cheap to get some quick cash he shouldn't have a problem. Take a look at this market depth chart for the Bitstamp exchange...
http://bitcoincharts.com/markets/bitstampUSD_depth.html
From what I see, if he's willing to accept $340 for them, he could sell 10,000 bitcoins straight away for an instant $3.4 million, and still have 25,000 bitcoins left.